Treatment of metal melts



May 8, 1962 F. HARDERS TREATMENT OF METAL MELTS Filed April 15, 1959.fm/eman' 6 'FR/TZ HARDERS M g M ATYOR/VEYS I 3,033,550 TREATMENT OFMETAL MELTS Fritz Harriers, Post Ergste, uber Schwerte (Ruhr), Germany,assignor to Dortmund-Hinder Hiittenunion Aktiengesellschait, Dortmund,Germany, a body corporate of Germany Filed Apr. 15, 1959, Ser. No.896,554 Claims priority, application Germany May 22, 1958 5 Claims. (Cl.256-34) For the vacuum treatment of metal melts, especially in thedegasification of steel, use may be made of an evacuated vessel which isarranged above a container which is under atmospheric pressure and isconnected to the container by a rising pipe which is filled with themetal melt during the treatment. the level of the melt in the containerand that in the evacuated vessel cannot therefore exceed the barometricheight which is determined by the specific gravity of the melt. Forsteel the barometric height is, on the average, 1.4 metres. If it isdesired to keep a substantial quantity of the melt in the evacuatedvessel during the treatment, the apparatus must be designed in sucha waythat the evacuatable vessel is disposed at only a small distance abovethe container which is under atmospheric pressure, and it must be bornein mind that the container frequently consists of a ladle filled with amelt and otherwise designed from the usual points of view. For these andother reasons it has not been possible to increase the amount of melt inthe evacuated vessel above a certain amount which is in no waysufficient.

Attempts have, therefore, been made to devise means whereby the distancebetween the level of the melt in the vacuum vessel, on the one hand, andin the container, which is under normal pressure, on the other hand, maybe increased so that this distance exceeds the barometric height.

Theoretically such an increase in height is actually possible byallowing a current of gas to flow through the melt in the rising pipe soas to impart as it were a certain amountof dynamic buoyancy to the melt.For this The difference between purpose a nozzle has been introducedinto the wall of the rising pipe through which nozzle a gas wascontinuously blown into the melt rising in the pipe. The effect of thisexpedient, however, has been found to be too small to be of practicalinterest. The possible increase in the distance between the levels ofthe melt in the vacuum vessel and in the container does indeedqualitatively meet the theoretical expectation but does not do soquantitatively would have practically justified the blowing in of gasinto the rising pipe. When this was done, however, the effect becamenoticeable only when a considerable quantity of gas was used and, whendegasifying steel, for example, it counteracted the effect of theprocess and led even to an undesirable increase in the necessary outputof the vacuum pumps and to an increase in the size of the vacuum vesselbeing necessary because the melt boils vigorously owing to the largeadditional amount of gas.

The invention is based on the discovery that the dynamic buoyancyproduced by the current of gas flowing upwardly in the rising pipe issuch as to be practically useful only if the current of gas isintroduced in such a way that it is distributed over the entirecross-sectional area of the rising pipe. If the process is carried outin this way it has been surprisingly discovered that even relativelysmall amounts of gas, which have no appreciable eifect when the knownmethod is used, effect a considerable raising of the level of the meltin the vacuum vessel. The explanation of this unexpected effect isprobably that a current of gas which is not distributed over the fullcross-section of the rising pipe only causes turbulence in the risingpipe but not buoyancy.

An apparatus for carrying the process of the invention into effect canbe constructed in many different forms. The most obvious way is toinsert a large number of nozzles through the wall of the rising pipe,the nozzles projecting to different distances from the wall. This,however, would lead to structural complications which could scarcely beovercome. It would also be possible to construct a part of the wall ofthe rising pipe of porous refractory brickwork through which the gas isblown. However, only by the use of very high pressures, which would notbe practicable, could the gas be driven so far radially inwards from thepores that it would be dis tributed over the entire cross-sectional areaof the rising These difiiculties are obviated by means of the inventionby using a gas inlet pipe having an outlet opening which opens below thelower opening of therising pipe. According to the invention, therefore,the place at which the gas is introduced into the melt is situatedoutside the rising pipe. It is, therefore, easily possible to form themouth of the gas inlet pipe in such a way that the gasv approximatelyequal in area to the cross-sectional area of V the rising pipe and toallow gas bubbles to enter rhythmically through this opening, the gasbubbles being so large that they entirely or nearly entirely fill thecross-sectional area of the rising pipe. It has been found, however,that the desired effectcan be considerably enhanced by introducing thecurrent of gas in a state of fine sub-division. This can be done byarranging at the outlet end of the gas inlet pipe at head having anumber of nozzles, the total cross-sectional area of which is preferablyat least half as great as the internal cross-sectional area of therising pipe.

A sufficient tine distribution of the gas current is obtained if thecross-section of an individual nozzle is, at the most, equal to 1 mm. Inthis case excellent results are obtained particularly if the nozzle headis made of refractory porous material.

As regards the shape of the nozzle head in other respects it isadvisable to make it conform in shape and size to the internalcross-sectional area of the rising pipe. The upward flow of the melt isnot interfered with by the nozzle head arranged below the mouth of therising pipe if the distance between the mouths of the rising pipe and ofthe gas inlet pipe is made approximately equal to or greater than'theinternal diameter of the rising pipe. The effect of the flow is then tohold together the rising streams of gas bubbles.

in many treatment processes the degasified melt in the vacuum vessel isreturned through the rising pipe to a ladle or container below it. Whenthis is done the nozzle head disposed below the mouth of the rising pipemay cause some interference. Since the uniformity of a vacuum treatmentdepends on -whether the degasified material can mix completely with themetal in the ladle,

or is, at least partly, disposed in a layer below this metal, it isparticularly advantageous ifthe degasified material on its return to theladle flows to the bottom thereof in a substantially closed stream andfirst distributes itself over the bottom so that mixing then takesplacefrom the bottom upwards. In order to prevent this advantageous actionbeing interfered with by the device for introducing the current of gas,according to the invention, the gas inlet pipe and its month are soarranged that they can be moved out of alignment with the rising pipe,for example by mounting the gas inlet pipe so that it can be swungaside.

An apparatus for carrying out the process of the invention isillustrated, by way of example, in the accompanying drawing which showsa longitudinal section through an apparatus for degasifying a steelmelt.

Referring to the drawing, the apparatus illustrated consists of a lowerladle 1 which is under atmospheric pressure and is provided with theusual closure plug and with a refractory lining 2, and an upper vessel 3which has a refractory lining 4 and can be closed on all sides and isconnected by a pipe 5 to a vacuum pump. The vessel 3 has a cover 6having a closable opening 7 through which other substances can, ifnecessary, be added in regulated quantity to the melt in the vessel 3.

The ladle 1 and the vessel 3 are in communication through a rising pipe8 which is protected on the inside and partly also on the outside by arefractory lining 1t and a refractory jacket 9. A curved pipe 11 extendsinto the container 1 and is suspended from a support 12. The support 12allows the pipe 11 to be swung about a vertical axis 13 and also permitsits height to be adjusted. The pipe 11, which is protected by arefractory covering 14 is provided at its lower open end with a hollowmember 15 of porous brick or stone which is disposed in alignment withand below the opening of the rising pipe 8. The pipe 11 is connected, bymeans not illustrated, to a vessel containing gas under pressure.

The steel to be degasified is charged up to the level a into theladle 1. After this, the vacuum pump connected to the pipe 5 is switchedon, so that the vacuum produced in the vessel 3 draws part of the steelfrom the ladle 1 into the vessel 3, whereby the level in the ladle islowered to the level [1. The distance between the levels of the melt inthe ladle 1 and in the vessel 3 now amounts to h;, an amount whichcannot be greater than the barometric height which, in the case of iron,only amounts on the average to 1.4 metres. Now, a valve which is notillustrated and is disposed between the pressure gas container and thepipe 11 is opened so that gas emerges in a finely divided form from theouter surface 17 of the member 15. The gas bubbles which are indicatedby dots in the drawing rise in the melt and arrive at the mouth 16 ofthe rising pipe 8 and then rise upwards in the pipe 8 until they arrivein the gas chamber of the vacuum vessel 3. This current of gas which isproduced in the form of finely distributed bubbles produces a dynamicbuoyancy, the result of which is that the distance between the level ofthe melt in the ladle and in the vacuum vessel rises from the originalmount I1 determined by the barometric height to the amount I1 and thelevel in the ladlevsinks to c. The drawing shows clearly the extent towhich the amount of melt in the vessel 3 is thereby increased.

After a certain time of treatment in the vessel 3 the vacuum isdisconnected so that the melt in the vessel 3 is returned to theladle 1. In order to prevent the gas pipe 11 and its hollow head 15 frominterfering with the return flow of the melt, the gas pipe 11 ispreviously swung laterally about the axis 13-, so that the nozzle head15 is disposed outside the extended axis of the rising pipe 8'.

The interchange of the portions of the melt in the vacuum vessel 3 withportions in the ladle 1 need not be effected by alternately connectingthe disconnecting the vacuum at 5. Instead of doing this it is possibleto increase and reduce the distance between the vessel '3 and the ladle1, that is to say to raise and lower either the vacuum vessel 3 or theladle 1. Then, in all cases, when the vessel 3 is emptied into the ladle1 through the rising pipe 8 the head 15 is swung aside. In the reverseprocess when the melt is returned through the rising pipe 8 into thevacuum vessel 3 the nozzle head 15 can at first remain in its swungaside position. However, in order to effect a more rapid charging of thevessel it is usually advantaigeous to bring the nozzle head 15 into itsswung-in position in alignment with the rising pipe 8 at the same timeas the inflow into the vessel 3 begins.

When the nozzle head is swung out, the current of gas which escapesthrough the pores in the nozzle 15 can, and should in general, bemaintained, in order that the pores may not be blocked by parts of themelt.

The effect of the cross-section of the gas inlet nozzle which, in theexample illustrated, is constituted by the pores of the nozzle member15, will finally be explained by means of a numerical example. With adiameter of 1 mm. the result could be obtained that the distance of thetwo levels exceeded the barometic height by 10 centimetres. This isalready considerable seeing that, in the arrangement illustrated, hamounts to about 1.4 metres. A reduction in the diameter from 1 mm. to0.2 mm., however, gave the surprising result that the increase in thedifference of level amounted to 50 centimetres. At the same time the gasconsumption fell from 50 cubic metres per hour to 5 cubic metres perhour, that is to say to onetenth of that which had to be used for 1 mm.diameter nozzles or pores for increasing the level by only 10centimetres.

The steel which flows from below into the rising pipe may, in somecircumstances, have a restrictive and compressive effect on the gasbubbles in the cross-sectional area. If the uniformity of thedistribution of the current of gas is too strongly impaired in this way,then additional gas can'be introduced from the inner surface of thepipe, so that a sufiicient number of gas bubbles also rise up in theedge zone and prevent the liquid steel from flowing back in this zone.

I claim:

1. Apparatus for the vacuum treatment of metal melt comprising a closedvessel, means for evacuating said vessel, a container for the meltdisposed below said vessel and under atmospheric pressure, a rising pipeforming the sole connection between said vessel and said container, theupper end of said pipe being connected to said vessel and the lower openend extending into said container, and a gas inlet pipe with its outletdisposed below, in alignment with, and spaced from the lower open end ofsaid rising pipe, said gas inlet pipe having a plurality of outletnozzles of small size relative to the cross-sectional area of saidrising pipe, said nozzles being uniformly distributed over an area theshape and size of which equals substantially that of the internalcross-sectional area of said rising pipe, whereby the gas is distributedover the crosssectional area of said rising pipe.

2. The apparatus as claimed in claim 1, in which the totalcross-sectional area of said nozzles is at least half the internalcross-sectional area of said rising pipe.

3. The apparatus as claimed in claim 1, said gas inlet pipe having anozzle head in which the cross-sectional area of any individual nozzleis at the most 1 mrn.

4. The apparatus as claimed in claim 1, said gas inlet pipe having ahead of porous refractory material.

5. The apparatus as claimed in claim 1, in which the distance betweenthe mouth of the gas inlet pipe and the mouth of the rising pipe is atleast equal to the internal diameter of the rising pipe.

References Cited in the file of this patent UNITED STATES PATENTS1,921,060 Williams Aug. 8, 1933 2,726,952 Morgan Dec. 13, 1955 2,848,317Coupette et al Aug. 19, 1958 2,852,246 Janco Sept. 16, 1958 2,854,333Thomas Sept. 30, 1958 2,871,008 Spire Jan. 27, 1959 2,893,860 LorenzJuly 7, 1959

1. APPARATUS FOR THE VACUUM TREATMENT OF METAL MELT COMPRISING A CLOSEDVESSEL, MEANS FOR EVACUNATING SAID VESSEL, A CONTAINER FOR THE MELTDISPOSED BELOW SAID VESSEL AND UNDER ATMOSPHERIC PRESSURE, A RISING PIPEFORMING THE SOLE CONNECTION BETWEEN SAID VESSEL AND SAID CONTAINER, THEUPPER END OF SAID PIPE BEING CONNECTED TO SAID VESSEL AND THE LOWER OPENEND EXTENDING INTO SAID CONTAINER, AND A GAS INLET PIPE WITH ITS OUTLETDISPOSED BELOW, IN ALIGNMENT WITH, AND SPACED FROM THE LOWER OPEN END OFSAID RISING PIPE, SAID GAS INLET PIPE HAVING A PLURALITY OF OUTLETNOZZLES OF SMALL SIZE RELATIVE TO THE CROSS-SECTION AREA OF SAID RISINGPIPE, SAID NOZZLES BEING UNIFORMLY DISTRIBUTED OVER AN AREA THE SHAPEAND SIZE OF WHICH EQUALS SUBSTANTIALLY THAT OF THE INTERNALCROSS-SECTION AREA OF SAID RISING PIPE, WHEREBY THE GAS IS DISTRIBUTEDOVER THE CROSSSECTION AREA OF SAID RISING PIPE.